The development of milk functional foods including health-promoting green tea polyphenols represents a challenge for the food industry since the formation of protein–polyphenol complexes may affect both protein technological properties and polyphenols biological activity. The present work aimed at the characterization of complexes formed between green tea polyphenols and either β-lactoglobulin (β-lg) or caseinomacropeptide (CMP), as well as to evaluate how this complexation may impact on protein gelation and polyphenol antiproliferative activity against tumor cell lines. Particle size and charge of protein–polyphenol complexes depend on protein nature and pH. At pH 6 they had the smallest size and were soluble. The presence of polyphenols accelerated the gelation of both β-lg and CMP, and mainly affected viscoelasticity of β-lg gels. Polyphenol complexation by proteins did not inhibit its anti-proliferative activity. Moreover, they exerted a better performance on some particular tumor cell lines.